When Greater Precautions Are Needed To Avoid Instrument Separations

Separating rotary instruments is more likely when increasing amounts of bending are required to first enter the canal orifices and then to negotiate to the apex.??These conditions are often present when attempting to cleanse and shape third molars. Not only are the canals likely to be curved, but access is often compromised with prebending of the instruments needed to gain canal entry. Another level of unpredictability is the sustainability of the patient to keep their mouths open wide enough and long enough to instrument the canals without involuntary closure and without warning. Using mouth props help, but many patients do not tolerate them well. In these situations rotary instrumentation poses increased risks of separation all of which can be avoided by employing the reamers in a handpiece oscillating at 3000-4000 cycles per minute or about 60 cycles per second.

This is the technique I used in shaping and cleansing the maxillary right third molar shown in this post. After gaining access with a No. 4 short-shanked round bur, I located three canal orifices that I negotiated to the apex using the 06/02 tapered stainless steel twisted reamers first in the oscillating handpiece to make sure of the patency of my entry followed by using them manually to accurately attain the correct length verified by the apex locator. After that with a sequence of 6% NaOCl, 17% EDTA and Irritrol irrigants, using the reamers in the oscillating handpiece I both negotiated to the apex and at the same time activated the irrigants along the length of the canals as I widened the canal preparations to a 35/02. From my experience where access is compromised and as a result the chances of instrument separation are increased, it is mandatory to use an instrumentation system that minimizes stresses to both the reamers (not files) and the teeth being treated, something that is accomplished using the oscillating reamers at high frequency.

Instruments that must first be bent to enter into a canal and then negotiate a curved canal, particularly a mesial canal, are subject to great amounts of stress when used in a rotary fashion. That is not the case when the arc of motion is limited to 30o degrees. The instruments remain intact allowing the dentist to apply them vigorously against all walls and apply increasing amounts of apically directed pressure to gain full length. As noted in the curved preparation of the mesio-buccal canal, we were able to prepare the full length to a 35/02 preparation without any noticeable distortions.

I find whenever any questionable situations arise they can always be addressed with the oscillating system. It is a safety valve that is employed anytime when what may be interpreted as excessive resistance to apical negotiation is encountered consistently preventing instrument separations. The minimal impact on the structural integrity of the instruments as well as its benign impact on the canal walls, in accordance with Newton’s Third Law of Motion, frees the dentist to use them in a way that encourages three-dimensional shaping with less likelihood of leaving debris behind in thin isthmuses and narrow buccal and lingual extensions.

The safety is inherent due to a system that generates short arcs of motion that nullify the impact of torsional stress and cyclic fatigue so intimately associated with rotary application of instruments and are the main factors leading to instrument separation and the production of dentinal micro-cracks.?

When we talk about alternative methods of instrumentation, as Einstein said we should make things as simple as possible, but no simpler. Imo, 30o oscillating reamers is a good example of that insightful statement.

Regards, Barry